I was able to determine my build date by patiently doing some research. Obviously I know the VIN number of my car so I went on eBay and Pelican and looked for cars for sale that were the same model year AND TYPE of my car (Example 1975 Targa.)

I created a database with verified build dates. When someone was selling a car I looked for a photo of the drivers door jamb where the original production sticker and made note of VIN and build date. Below are a couple of examples of two such VIN stickers I found while searching vehicles for sale.

After a month and a half I was able to narrow down the month/year of production based on my database. Example: You can assume a vehicles with the VINs between 911521-0089 and 911521-0101 were manufactured in July 1974 Since their VINs fall between two known/verified vehicles that were built in July 1974.